TanDEM-X Mission Status, Products and Perspectives

TanDEM-X is an innovative single-pass interferometric radar mission, which is comprised of two formation flying satellites. The TerraSAR-X (TSX) satellite was launched on June 15th 2007, and its almost identically constructed twin satellite TanDEM-X (TDX) was launched on 21st of June 2010. Together they supply high-quality radar data in order to serve two main mission goals: Scientific observation of the Earth and provision of remote sensing data for the commercial market (TerraSAR-X mission), and the generation of a global digital elevation model (DEM) of the Earth's surface (TanDEM-X mission). Between December 2010 and early 2015, radar data of all land surfaces has been acquired and as of September 2016 the final TanDEM-X DEM dataset has been available. This paper provides a final quality assessment of the TanDEM-X global DEM products with respect to the relative and absolute height accuracy and data coverage both at the global and geocell level. In addition, an overview on current mission status is given and new DEM products, which are currently in the scope of the TanDEM-X mission, are described

A Decade of TerraSAR-X and TanDEM-X Operation: A Retrospective on the Performance of the SAR System and an Outlook to the Future

TerraSAR-X and its almost identical twin satellite TanDEM-X have provided high resolution radar images for years and Digital Elevation Models with unprecedented accuracy. The SAR image quality and accuracy has remained constant since launch and is owed to a very stable instrument. A thorough system health monitoring is utilized in order to maintain this stability. On the one hand a short-term verification of the individual acquisitions constantly exploits satellite telemetry from the SAR instrument and the on-board calibration system. Hence performance hanges, e.g. in terms of hardware degradation, can quickly be identified and corrected. For example by monitoring the antenna’s T/R modules via pseudo noise gating, dysfunctional modules could be detected in order to re-adjust the system accordingly. On the other hand a long-term system monitoring approach furthermore was designed to detect long-term system parameter trends and degradations that may affect data quality or imaging capabilities. In particular on-ground measurements are evaluated by continuously imaging globally distributed reference targets such as corner reflectors or test sights with a well-known topography. It was initiated with the launch of TerraSAR-X thus provides a variety of long-term parameter time series. Stimulated by this approach a study has been conducted to analyze the impact of solar events like radiation or the annual eclipse due to the satellites’ orbit geometry. Although the effects are taken into account by calibration the results provide valuable information to interpret monitoring results and gain a deeper understanding of the system. Besides retrospecting the SAR system the goal of this paper is also to give a summary of the TerraSAR-X and TanDEM-X mission with focus on the calibration and the systems’ functionality. The mission status will concentrate mainly on the performance of the global Digital Elevation Model which was completed in September 2016. Having used precise calibration methods and improved processing algorithms, the dataset shows an outstanding quality. In the end up to 20.000 tiles with a size of 1° x 1° were generated yielding an overall absolute height accuracy of 3.5 meters and covering more than 99% of the globe. As the satellites are still in good condition and consumables are sufficient, the mission was extended to generate a change layer as an update of the global DEM. By adjusting acquisition strategies and processing methods, fewer acquisitions are sufficient to achieve the same accuracy as for the global DEM. Furthermore, a brief outline of the proposed future L-band satellite formation is drawn. The ambitious mission shall provide data to help solving pressing climate-related questions. As an example the proposed system will be able to penetrate forest canopy in order to estimate biomass on a global scale. Equipped with a reflector antenna and exploiting the innovative digital beamforming technique, Tandem-L will be capable of illuminating a 350 km wide swath on ground acquiring up to 8 terabyte of data per day. This enables a weekly global coverage, which is a precondition for observing dynamic processes in the bio-, geo-, hydro- and cryosphere

TanDEM-X Height Performance and Data Coverage

TanDEM-X is a single-pass radar interferometric mission, which is comprised of two formation flying satellites, with the primary goal of generating a global Digital Elevation Model (DEM) of unprecedented accuracy. Between December 2010 and early 2015 all land surfaces have been acquired at least twice, difficult terrain up to seven or eight times and as of September 2016 the final TanDEM-X DEM dataset is available for download. This paper provides a final quality assessment of the TanDEM-X global DEM products with respect to the DEM relative and absolute height accuracy and data coverage both at the global and geocell level

TanDEM-X Voids Coverage Evaluation

The purpose of this document is to record the findings of the TanDEM-X DEM voids working group and the approach that will be used for the validation of the voids requiremen

Height Accuracy for the First Part of the Global TanDEM-X DEM Data

The TanDEM-X system is an innovative radar mission, which is comprised of two formation flying satellites, with the primary goal of generating a global Digital Elevation Model (DEM) of unprecedented accuracy. TanDEM-X, being a large single-pass radar interferometer, achieves this accuracy through a flexible baseline selection enabling the acquisition of highly accurate cross-track interferograms that are not impacted by temporal decorrelation or atmospheric disturbances. At least two global coverages (four in the case of difficult terrain) are combining into a homogenous global DEM mosaic consisting of 1° by 1° geocells. This paper provides a quality summary of the currently available part of the TanDEM-X global DEM with respect to the DEM absolute and relative height accuracy as well as to void density per geocell

Height Accuracy and Data Coverage for the Final Global TanDEM-X DEM Data

TanDEM-X is an innovative single-pass radar interferometric mission, which is comprised of two formation flying satellites, with the primary goal of generating a global Digital Elevation Model (DEM) of unprecedented accuracy. Between December 2010 and early 2015 all land surfaces have been acquired at least twice, difficult terrain up to seven or eight times and as of September 2016 the final TanDEM-X DEM dataset is available for download. This paper provides a final quality assessment of the TanDEM-X global DEM products with respect to the DEM relative and absolute height accuracy and data coverage both at the global and geocell level

Generation of a global forest/non forest map from TanDEM-X interferometric data

Generation of a Global Forest/Non Forest Map from TanDEM-X Interferometric Data Christopher Wecklich, Michele Martone, Paola Rizzoli, Gerhard Krieger The remote sensing data that the TanDEM-X system is providing represent a highly valuable source for land classification purposes. A precise and up-to-date knowledge of the land cover information is of great importance for a wide range of scientific and commercial purposes. In particular, the identification and the monitoring of vegetated areas is critical for a variety of applications, such as agriculture, cartography, geology, forestry, global change research, and for regional planning. This paper presents an overview of the forest cover map being generated from the global TanDEM-X quicklook dataset, which are multilooked and re-quantized versions (50 m x 50 m) of the full resolution data. A detailed description of the generation method of a forest/non-forest classification map from individual TanDEM-X interferometric SAR scenes, by exploiting the volume decorrelation contribution, which characterizes forested areas, will be presented. Volume decorrelation represents the interferometric coherence loss which is caused by multiple backscattering within a volume and is predominantly affected by the presence of vegetation. Given a coherence estimate, it is possible to estimate the volume decorrelation contribution and this characteristic can be used to distinguish vegetated areas from non-vegetated ones. A clustering approach based on fuzzy logic is utilized for partitioning each pixel into two classes: forest or non-forest, by associating to it a membership value to each single class. Furthermore, the method for the mosaicking of the overlapping scenes to generate a global forest map will be presented. To accomplish the final mosaic, multiple coverages over the same area are properly combined together by performing a weighted average which takes into account quality indicators of their reliability, such as the dependency of volume decorrelation on the height of ambiguity and the SNR. The inclusion of the SNR component in the weighting logic reduces the influence of the pixels on the edge of each scene where the SNR is reduced, due to a lower antenna gain. Various additional layers are derived and applied on top of the forest/non-forest map, for example to remove urban areas and water pixels, before the pixels are finally mosaicked together. The final product will be a forest/non-forest map with a 50 m x 50 m resolution and global coverage. To conclude the paper, the validation and performance measurement approach using ground truth maps and independent sources and preliminary results will be described and discussed

Height Accuracy and Data Coverage Status of the Global TanDEM-X DEM

TanDEM-X is a single-pass radar interferometer mission, which is comprised of two formation flying satellites, with the primary goal of generating a global Digital Elevation Model (DEM) of unprecedented accuracy. This paper provides a quality summary of the TanDEM-X global DEM products available from February 2016 with respect to the DEM relative and absolute height accuracy and data coverage both at the global and geocell level

Production of a Global Forest/Non-Forest Map Utilizing TanDEM-X Interferometric SAR Data

In this paper we describe the method that has been implemented to derive the forest/non-forest maps from TanDEM-X interferometric synthetic aperture radar (InSAR) data, globally acquired in stripmap single polarization (HH) mode. Among the several observables systematically provided by the TanDEM-X system, the volume decorrelation contribution, derived from the interferometric coherence, shows to be consistently sensitive to the particular land cover type, and is therefore used as an input data set for applying a classification method based on a fuzzy clustering algorithm. Since the considered InSAR quantity strongly depends on the geometric acquisition configuration, namely the incidence angle and the interferometric baseline, a multi-clustering classification approach is used. Once the Forest/NonForest classification for individual acquisitions is generated, overlapping acquisitions are mosaicked together to improve the resulting accuracy. The final step in the Forest/NonForest map production is to apply a binary Forest/Non-Forest decision and the decision threshold is found through comparison with similar data and statistical analysis. Verification and validation of the final product will be accomplished through comparison to other forest maps. In summary, this paper covers the processing and production status of the global TanDEM-X Forest/Non-Forest map which will be made available to the scientific community in 2017